To contain electromagnetic radiation (EMR, sometimes referred to as EMI for electromagnetic interference) in an electronics enclosure, such as a computer housing, an effective Faraday cage has to surround the emitting sources of radiation. In general, this is achieved by enclosing the emitting sources in a conductive enclosure and limiting the size of and shape of any openings in that enclosure to a size that will not pass significant levels of electromagnetic energy.
Peripheral Component Interface (PCI) and PCI Express® (PCIe®) refer to high speed computer interface bus standards with defined connector and interface panel (“backplate”) mechanical form factors. Modules designed to this standard are more generally referred to as expansion cards, and generally comprise removable subassemblies designed to be easily installed or removed from an enclosure, sometimes in the form of a card cage, that holds the cards in place. When installed in the enclosure, the interface connections of the subassembly are typically accessible from the outside of the enclosure through the backplate. This allows external cabling and the like to be connected to a PCI/PCIe® module.
The size and shape of the openings in the enclosure that accept an expansion cards are defined by the industry standards, as is the conductive backplate (panel) that is the part of the module arranged to cover the opening in the enclosure when the PCI/PCIe module is installed. For state of the art electronics, and the radiating frequencies generated thereby, the conductive connection between the PCI/PCIe module's interface conductive panel and the conductive surfaces of the enclosure containing the associated openings, as defined by the industry standards, can be insufficient in suppressing the EMR radiating from the enclosure to acceptable levels.